A conventional approach to the problem as applied to such installations as grease traps and septic tanks is to provide sufficient volume and separation of inlet and outlets with appropriate baffles to have sufficient holding time of the liquid and insoluble materials for separation to occur naturally. However, this process is not entirely reliable and contamination of e.g. sewer lines or absorption trenches can occur. This is especially the case where it is necessary or simply desirable to have a vessel of relatively small dimensions and a frequent problem occurs where there are major surges of flow into the vessel. Surges can produce turbulence and the rapid increase of liquid in the vessel displaces a corresponding volume rapidly through the discharge line. Thus entrainment of both buoyant and non-buoyant contaminants can all too easily occur.
For exemplification only the invention will be described and with reference to grease traps but it is to be understood the invention is not so restricted and applies to all similar installations.
Generally, commercial establishments such as restaurants are obliged to install and maintain a grease trap for waste water and at regular intervals the grease trap will need to be pumped free of major build ups of both buoyant and non-buoyant contaminants. Filter type units have been extensively employed to try and control unintended discharge of contaminants into the waste water and such filter units have been positioned around the normal liquid level and generally have been of a removable cartridge type. In a typical restaurant type facility a grease trap must be pumped to remove contaminants every few weeks and the contractor should also change the cartridge type filter. However, the expense of grease trap servicing is significant and proprietors will be tempted to remove filters to ensure longer time between serving. If the filter is not regularly serviced, then there is likely to become clogging due to greases at the surface of the liquid in the vessel and, especially under the surge conditions which frequently arise, waste water may flood back into the premises.
One form of such filter comprises a rigid collection of shaped plates which have apertures between the plates to provide the filter structure. The plates are disposed horizontally and the cartridge has a vertical axis. An example of such as filter is that of U.S. Pat. No. 4,710,295 (Zabel).